Obstacle detection systems for providing an indication of the distance and/or warning of nearby objects have been proposed. One application for such systems is for detecting objects in proximity to an automotive vehicle. For example, the vehicle may employ a near obstacle detection system to alert the vehicle operator of the presence of obstacles behind the vehicle while backing the vehicle, to alert the vehicle operator of any obstacle in front of the vehicle below the operator's line of sight or to alert the operator of approaching vehicles in areas that are out of the view of the rear and side view mirrors.
Characteristics that are desirable in near obstacle detection systems include: (a) the ability to warn of obstacles having no motion relative to the detection system, (b) the ability to detect the closest of multiple objects, (c) the ability to provide a measure of distance to the object even at very close distances, and (d) the ability to operate in all environmental conditions.
Various systems have been proposed for near obstacle detection. One such system is based on the Doppler signal resulting from relative motion between the system and the object. As applied to a vehicle, this means that the system could not warn the driver of a passive obstacle behind the vehicle until the vehicle operator has initiated backward movement.
Ultrasonic and infrared near obstacle detection systems have also been proposed. Ultrasonic systems may be sensitive to wind noise and other ultrasonic noise sources and are constrained by the speed of sound while infrared systems suffer from back scattering caused from hydrometers and aerosols, sensitivity to object color and from contamination of the optical surfaces.
On the other hand, a frequency modulated continuous wave (FMCW) microwave radar system has all of the above listed desirable characteristics. However, present FMCW near obstacle detection systems require a large RF bandwidth in order to sense the range of objects very close to the radar system. For example, in present FMCW systems, a bandwidth of 500 MHz is required to sense an object at a range of 0.3 m, which is also the range resolution of the system. It would be desirable to decrease the bandwidth of an FMCW near obstacle detection system and thereby retain the desirable characteristics of such systems without increasing the minimum detection range of the system.